Unloader for reciprocating gas compressors



Jan. 11, 1949. w, bopso 2,458,933

UNLOADER FOR RECIPRQCATING GAS COMPRESSORS Filed Dec. 18. 1946 2She'ets-Sheet 1 v I nvenc or:

Wayne El. Dodson.

' His Attorney.

Jan. 11, 1949.

w. E. DODSON UNLOADER FOR RECIPROCATING GAS COMPRESSORS 2 Shoots-Sheet 2Filed Deg. 18, 1946 van .l lll I n ventorfv Wayne E3. Dodson, by M 1124*His Attorney.

Patented Jan. 11, 1949 UNLOADER FOR. RECIPROCATING GAS coMPaEssoas WayneE. Dodson, Caldwell, N. J., assignor to General Electric Company, acorporation of New York Application December 18, 1946, Serial No.717,002

My invention relates to reciprocating gas compressors and particularlyto an improved unloading arrangement for such compressors.

Gas compressors may be unloaded by providing a bypass for the return ofcompressed gas directly from the discharge to the intake of thecompressor. A check valve may be provided to prevent the return of highpressure gas from the system served by the compressor when the bypass isopened. In multiple cylinder reciprocating compressors the load on thecompressor may be changed by unloading one or more'of the cylinders, andin such compressors a check valve is necessary at each cylinder or groupof cylinders to be unloaded so that the compressed gas supplied by theloaded cylinders cannot return Claims. (Cl. 230-22) air or other fluidcirculated thereover, and the I hot compressed refrigerant therein isthus cooled and liquefied and is then delivered to a receiver 1. Theliquid refrigerant flows to the evaporator 5 through a liquid line I!under control of a thermostatic expansion valve 9 having a thermal bulbThe check valves provided for this and having a check valve forpreventing back flow of compressed refrigerant gas during unloadedoperation of the compressor.

Further objects and advantages of my inven tion will become apparent asthe following description proceeds, and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of my invention reference may be had to theaccompanying drawings in which Fig. 1 represents diagrammatically afluid cooling system provided with a compressor embodying my invention,and Fig. 2 is a detail sectional view of one of the cylinders of-thecompressor of Fig. 1 including the bypass control.

Referring now to the drawings, the cooling system shown in Fig. 1comprises a multiple cylinder compressor having cylinders I and 2connected in parallel to deliver refrigerant to a condenser I and towithdraw vaporized refrigerant through a suction line I from anevaporator 5. In order to simplify the drawing, the driving mechanismfor the compressor has been omitted, it being understood that pistons inboth cylinders I and 2 may be driven from a common crankshaft in theusual manner. The evaporator 5 is arranged in a duct or conduit 8through which the medium to be cooled is circulated. The condenser 3 iscooled by or ieeler l0 secured to the suction line 4 near the outlet ofthe evaporator.

During the operation of the system illustrated,

should the load on the evaporator 5 be greatly reduced it may bedesirable to reduce the effective capacity of the compressor, and inorder to reduce the capacity without discontinuing operation ofthe'compressor a bypass Ii is provided between the discharge chamber ofthe cylinder 1 within a head l2 of the cylinder and the suction line 4,the bypass l I being controlled by a valve i3 actuated by a solenoid ll.The solenoid i4 is arranged to be energized by operation of a snapactingor over-center switch l5 when the pressure within the suction line 4falls below a predetermined value and causes a bellows I6 which is incommunication with the line 4 through a duct ll to contract asillustrated and actuate the switch i5 through a rod i8 which pulls aspring i9 over center to snap the switch i5 from its right-handposition, to its left-hand position (as shown) to energize the solenoidIt by connecting it across supply lines 20. Energization of the solenoidl4 opens the valve is so that the cylinder i pumps refrigerant gasdirectly back to the suction line through the conduit H and the onecylinder is thus unloaded.

Although the control switch i5 has been illustrated as operated inaccordance with suction line pressure, it obviously may be operatedmanually or by any condition of the system suitable g} for indicatingthe requirement for unloading.

The details of construction of the cylinder i and the arrangement of thebypass are clearly shown in Fig. 2. The cylinder i comprises a block 2ihaving a cylinder 22 therein and a piston 23 arranged to bereciprocated'within the cylinder. A valve plate 24 is mounted on top ofthe cylinder and on this plate are arranged intake and exhaustconnection ii. The head I2 is formed to provide a discharge chamber orpassage 32 above the 3 valve 28 and a passage 33 separated from thepar;-

sage 32 by a partition 34; the passage 33 is in duit II to the suctionline 4 is controlled by the valvei3 which includes a movable valvemember 39 for controlling a port 40 in the valve body.

When the'solenoid I4 is energized to move the valve member 39 to itsopen position against the force of a spring 39a, gas discharged into thechamber 32 is delivered to the suction line 4 through'the conduit I sothat the chamber 32 is connected to the inlet passage 29 through theconduit i l, the suction line 4 and the conduit 30.-

In order to prevent thereturn of compressed gas from the connection 35,which is in communication with the condenser 3, a check valve 4| isarranged to close an opening 42 in the partition 34. The check valve 4|comprises a piston mounted in a cylinder 43 at the top of the head l2and which is closed by a head plate 44. The cylinder 43 and piston 4|are arranged for vertical movement of the piston so that the check valveis biased by gravity to its lower position to close the opening 42. Thepiston 4| is provided with a cylindrical cavity or chamber 45 which isin communication with the high pressure passage 33 through a duct orbleeder 46. Thus when the valve 4| is in its lower position, highpressure gas enters the cylinder 43 and holds the valve closed. It willthus be evident that when the bypass valve 39 is open, as shown in Fig.2, the check valve 4| is held in its closed position, the pressure inthe chamber 32 being that on the low pressure side of the refrigeratingsystem.

When the valve 33 is closed to load the cylinder 22 of the compressor2|, the gas discharged into the chamber '32 will reach a pressure higherthan that in the passage 33 and will lift the check valve 4| allowingthe gas to be discharged from the compressor through the connection 35.The operation of the check valve 4| when the compressor is loaded mayresult ln'chattering of the valve and consequent noise and wear, whichis objectionable. In order to prevent this chattering and wear of thevalve, I provide a conduit 41 connected betweenthe suction line 4 andthe cylinder 43 under control of a manual valve 48 and a valve 49actuated by a solenoid 50. As shown in Fig. 1, the solenoid 50 isenergized when the switch I is in its right-hand position. Thustheswitch l5 energizes only one of the solenoids l4 and 50 at a time sothat only one of the conduits II and 41 can be open at one time. Whenthe valve 49 is opened, the cylinder 43 is in communication with thesuction line and the pressure in the cylinder is reduced so that thepiston valve 4| is retracted and held in its retracted position duringthe loaded operation of the compressor. The manual valve 48 may beadjusted to control the bleeding of gaseous refrigerant through thepassage 46, cylinder 43 and conduit 41 back to the suction line and inthis manner the capacity of the compressor which is lost during loadedoperation may be reduced or noise will result during the loadedoperationofthe compressor and wear or the check valve provided a simple.and effective arrangement which makes it possible to employs. checkvalve to prevent return of compressed gas toan unloaded cylinder of amulticylinder compressor without resultant noise or chattering of thecheck valve during loaded operation of the compressor.

' While I have described my invention in con-' nection with a.two-cylinder compressor for supp ying a refrigerating system, otherapplications will readily be apparent to those skilled in the art. I donot. therefore, desire my invention to be limited to the specificconstruction illustrated and described, and I intend by the appendedclaims to cover all modifications within the spirit and scope oi-myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A reciprocating gas compressor comprising a cylinder having intakeand discharge valves, means providing intake and discharge passagesadjacent said intake and discharge valves respectively, an outletconnection communicating with said discharge passage, bypass meansprovldingcommuuication between said discharge and intake passages forunloading said cylinder, means for closing said bypass to load saidcylinder, 9. check valve for preventing return of gas through saidoutlet connection to said discharge passage upon opening of said bypass,and means rendered efiective upon the loading of said cylinder forretaining said check valve in its open position to prevent vibration ofsaid check valve. I

2. A reciprocating gas compressor comprising a cylinder having intakeand discharge valves, means providing intake and discharge passagesadjacent said intake and discharge valves respectlvely, an outletconnection communicating with said discharge passage, bypass meansproviding communication between said discharge and intake passages forunloading said cylinder, means for closing said bypass to load saidcylinder, 2. check valve for preventing return of gas through saidoutlet connection to said discharge passage upon opening of said bypass,and means effective during the loaded operation of said compressor andutilizing the diiierence in pressure between the inlet an outlet of saidcompressor for retaining said check valve in its open position.

3. A reciprocating gas compressor comprising a cylinder having intakeand discharge valves. means providing intake and discharge passagesadjacent said intake and discharge valvesrespectively, an outletconnection communicating with said discharge passage, bypass meansproviding communication between said discharge and intake passages forunloading said cylinder, means for closing said bypass to load saidcylinder, a check valve for preventing return of gas through said outletconnection to said discharge passage upon opening of said bypass, saidcheck valve including means providing a closed cylinder and a pistonarranged therein, said closed cylinder having limited communication withsaid outlet connection whereby said valve is held closed by the pressureof gas in said closed cylinder, and means efiective during the loadedoperation of said compressor for reducing the pressure in said closedcylinder to maintain said check valve in its open position when saidbypass is closed.

4. A reciprocating gas compressor comprising a cylinder having intakeand discharge valves. means providingintake and discharge passagesadjacent said intake and discharge valves respectively, an outletconnection communicating with said discharge passage, bypass meansproviding communication between said discharge and intake passages forunloading said cylinder, means for closing said bypass to load saidcylinder, a check valve for preventing return of. gas through saidoutlet connection to said discharge passage upon opening of said bypass,said check valve including means providing a closed cylinder and apiston arranged therein, said closed cylinspectively, an outletconnection communicatingwith said discharge passage, bypass meansproviding communication between said discharge and intake passages forunloading said cylinder,

a check valve for preventing return of gas,

through said outlet connection to said discharge passage upon opening ofsaid bypass, said check 25 Number valve including means providing aclosed cylinder and a piston arranged therein, said closed cylinderhaving limited communication with said outlet whereby said valve is heldclosed when the pressure in said connection is greater than that in saiddischarge passage, means connecting said closed cylinder with saidintake passage to bleed refrigerant from said discharge connection tosaid intake passage to reduce the pressure in said closed cylinder forretaining said check valve in its open position,a control valve for saidconnection to said closed cylinder, and means for maintaining each ofsaid control valves in its closed position when the other of saidcontrol valves is in its open position whereby said check valve iseffective only during the period when'said compressor is unloaded.

WAYNE E. DODSON.

REFERENCES CITED I The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Kinney Apr. 5, 1927 Swartwout Aug. 11,1931 Swanson et al Man-1, 1932 Hirsch Aug. 30, 1932 Lindsay Jan. 9, 1934

